This invention relates to the suppression of noise due to static and/or mobile electromagnetic incompatibility.
Complex communications, radar and broadcast systems are always associated with metal structures. Examples are aerial masts and guys, building structures, ships or aircraft etc., on which the system is mounted. When metal structures are irradiated by high power transmitters, non-linearities at metal junctions in the structure cause the generation of harmonic and intermodulation products. These products are re-radiated by the metal structure, and are picked up by near by radio receivers as interference, even though the receivers are tuned to frequencies other than those of the offending transmitters. A large number of harmonic and intermodulation product frequencies can be generated by the effect, particularly in compact multi-transmitter sites, such as ships, and a large number of receiving channels can be blocked. Furthermore if metal junctions are intermittent or subjected to movement or vibration, wide band noise interference can be generated and re-radiated when the structures are irradiated. This give rise to a substantially increased noise level across the whole receiving band and the effect can be caused by only one transmitter. The above effects have generally been refered to as `the Rusty Bolt effect` and also as `SEMIC` and `MEMIC` (Static Electro-Magnetic Incompatibility and Mobile Electro-Magnetic Incompatibility). There are well documented cases of the effect causing severe communications problems with ship communications, radar, vehicle communications installations, airborne communications and navigation, communications satellites and radio broadcast relay stations.
An existing method of `Rusty Bolt effect` interference reduction is to bypass all metal junctions with a short spot welded metal strap (welded metal junctions do not generate interference when irradiated by RF). This method, is clearly laborious and not convenient.